settings.php

<?php

$this->EE->addon_settings = array(
    1 => array( // site_id
        'addon_name' => [json object]
    ),
    
    2 => array(
        'addon_name' => [json object]
    )
);


// Get add-on settings with:

$settings = $this->EE->addon_settings->get('addon_name', $site_id /* optional, defaults to current site_id */);